Office (OOXML) / .XLSX malware analysis — malicious · b984efd19fbe9948

MALICIOUS

Office (OOXML) / .XLSX

105.4 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000

MD5: ca2e9654a91c0f652ee5f9aa074b0276 SHA-1: 7a511f1fb073e2074102d3722e0422d6de2952a5 SHA-256: b984efd19fbe99484dac032cd182e5bfbb4a81a32bba8eb9e0d0217596f75b92

60 Risk Score

Malware Insights

MITRE ATT&CK

T1059.005 Visual Basic

The critical heuristic firing indicates the presence of an Excel 4.0 macro sheet. Analysis of the embedded macro content reveals it attempts to write a file to 'C:\ProgramData\excel.rtf', likely to download and execute a second-stage payload. The macro's obfuscated nature and truncated content limit further analysis, resulting in a lower confidence score.

Heuristics 1

Excel 4.0 macro sheet (1 sheet(s)) critical OOXML_XLM_MACROSHEET

Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.

Extracted artifacts 1

Files carved from inside the sample during analysis.

Filename	Kind	Source	Size
`xlm_sheet_00.bin` `10f4652d269ded98aafaef1407695398110112f1f29644a8e1e9af37c006bd85`	xlm-macrosheet	OOXML XLM macro sheet: xl/macrosheets/sheet1.bin	266738 bytes

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